Abstract: The Pingxiang red-transparent crucian carp,Carassius auratus(L.),which was approved for a new kind of breed by the National Fisheries thoroughbred Examining Committee in January 2008,is a wildness natural triplod crucian carp mutant distributed in the area of Pingxiang in Jiangxi Province.It takes bi-sexual and gynogenetic reproduction mode which is similar to the Silver crucian carp,Carassius auratus gibelio(Bloch).In response to this particular genetic traits of the species,this study aimed to master its gonadal development process and understand its gonadal development rules and characteristics,with a view to provide important reference value of the basic data for the developmental genetics of fish and the theoretical basis for guiding production for the breeding,raising and further improved breeding of the Pingxiang red-transparent crucian carp.The gonad development of the mutant of its F5 offspring was studied by sampling every month since hatching.We sampled a total of 12 months,each 20,and carefully stripped the ovarian section each time,measured their lengths,widths and thicknesses(3 months later),and statisticed the relative bearing-egg volume of the 12-month-old fish.The calculation method was as follows: the number of eggs per gram of ovary was counted,then its average was statisticed based on a total of six time radom-count.All materials were fixed using Bouin's solution,paraffh embedded according to conventional methods,sectioned and stained with haematoxylin and eosin.The slices were observed and took photos under the Leica DM5000B microscope,whereas,the mature individuals testis were selected for observation(the methods as above).Result indicated that the normal sexual maturation period was about one year.The process of development of the ovary could be classified as 6 stages and the oocyte could be divided into 6 phases.The annual variation of the maturation coefficient of the ovary was also counted.For a female fish with an average body weight of around 95 g,the maturation coefficient of its ovary was about(11.73±2.8) %.The mature ovary was full of yolks.The number of eggs per gram of ovary was about(3018±310) eggs.There were two rapid growth period for ovary,one was 4—8 months old and the other was 10—12 months old.The spermary was lobular type.Different developmental phases of germ cells could be observed in Seminiferous lobules.The primary spermatocytes mitosised from spermatogonia reproduce to the secondary spermatocytes and develop into spermatids at last.The testis development process of Pingxiang red transparent crucian carp was similar to the common carp.Most experimental individuals could achieve to sex maturation.The developmental course of the reproductive organs(ovary and testis) was basically synchronous.Differentiation of the gonad was not distinct 50 days after hatching,but began to show male and female distinction around 70 days after hatching.It developed into the first stage after 3 months,to the second stage after 4—5 months,and to the fourth ovary stage after 7—10 months.The gonad of the fish became mature in one year.The result indicated the gonadal development in natural wildness triploid mutant Pingxiang red-transparent crucian carp,which had been known for its gonochoristic and gynogenetic reproduction manners,was similar to the diploid common carp.